Mercury (Hg) is the third most important contaminant on the CERCLA Priority List of Hazardous Substances (2011) and its organic and toxic form, methyl mercury (MeHg), is a potent toxin with human health effects. Marine fisheries particularly in coastal ecosystems are dominant sources of human exposure to MeHg through consumption of marine fish and shellfish. 48 states in the U.S. have issued advisories against consumption of fish due to MeHg, including coastal advisories for the Atlantic Coast and the Gulf of Mexico. Sub-populations most at risk for exposure include pregnant women and children and subsistence fishers. To date, research on MeHg fate has not investigated the interaction of climate change variables such as temperature and nutrient/carbon loading even though they are likely to have synergistic effects on the formation and transfer of MeHg to the fish and shellfish that humans consume. The investigators therefore propose to examine in detail individual and combined effects of these factors using laboratory and field studies, and through integrative modeling to examine their overall impact on human exposure to MeHg. The following three aims are the basis for their primary hypotheses: Aim 1: Determine the effects of temperature, nutrient and carbon loading on the net MeHg formation in sediments and the associated net inputs of MeHg to the water column in coastal ecosystems. Aim 2: Determine the interactive effects of temperature and nutrient supply/ecosystem eutrophication on bioaccumulation of MeHg by primary producers, and transfer between primary and secondary consumers in estuarine food webs. Aim 3: Predict how climate-induced changes in MeHg bioaccumulation in coastal food webs will increase exposure and risk to sensitive populations. The investigators will apply innovative experimental and field techniques to investigate the interactions between these factors on MeHg fate in estuaries. They will investigate sites in northern and southern latitudes to determine the influence of a natural range of temperatures on MeHg production and bioaccumulation in estuarine ecosystems. Finally, they will use experimental and field data to adapt and parameterize an existing MeHg biogeochemistry and bioaccumulation model to include variation in temperature and nutrient/carbon loading. These tools will allow them to predict the effects of climate change variables on MeHg production and transfer to fish to estimate the net effect of these changes on human exposure.